Fluid pressure controls for transmission, clutch and brake



y 1957 D. J. K. STUART ETAL 3,322,245

FLUID PRESSURE CONTROLS FOR TPANSMISSION, CLUTCH AND BRAKE y 1967 D. J. K STUART ETAL 3,322,245

FLUID PRESSURE CONTROLS FOR TRANSMISSION, CLUTCH AND BRAKE 7 Sheets-Sheet 2 Filed June 21; 1965 May 30, 1967 D. J. K. STUART ETAL 3,322,245

FLUID PRESSURE CONTROLS FOR TRANSMISSION CLUTCH AND BRAKE Filed June 21, 1965 7 Sheets-Sheet 5 D J. K. STUART ETAL May 30, 1967 FLUID PRESSURE CONTROLS FOR TRANSMISSION, CLUT CH AND BRAKE 7 Sheets-Shet 4 Filed June 21, 1965 is? WNN May 30, 1967 D. J. K STUART ETAL 3,322,245

FLUID PRESSURE CONTROLS FOR TRANSMISSION, CLUTCH AND BRAKE Filed June 21, 1965 7 Sheets-Sheet 5 l "91 fig 9. a94- y 1957 D. J. K. STUART ETAL 3,322,245

FLUID PRESSURE CONTROLS FOR TRANSMISSION, CLUTCH AND BRAKE 7 Sheets-Sheet 6 Filed June 21, 1965 y 1967 D. J. K. STUART ETAL 3,322,245

FLUID PRESSURE CONTROLS FOR TRANSMISSION, CLUTCH AND BRAKE 7 Sheets-Sheet Filed June 21, 1965 United States Patent Ofitice 3,322,245 Patented May 3t), 1967 England Filed June 21, 1965, Ser. No. 465,323 Claims priority, application Great Britain, June 24, 1964, 26,07 64 21 Claims. (Cl. 192-.09)

This invention relates to change-speed power transmission mechanisms, and has an object the provision of such a mechanism in a convenient form.

A mechanism according to the invention comprises an input member, a driving shaft, means for drivingly interconnecting the input member and the driving shaft and including a clutch, a driven shaft, means drivingly connccting said driven shaft to an output member, a toothed control member one one of said shafts and axially movable between first and second positions to provide first and second speed ratios respectively, a fluid operable motor connected to the output side of said clutch, through the intermediary of a unidirectional drive device arranged so that, in use, no drive is transmitted from said clutch to said motor, a pump for supplying operating fluid to said motor to drive the latter, means sensitive to the pressure at which fluid is supplied to the motor and means operable by said pressure-sensitive means for moving said toothed control member when the clutch is disengaged and the pressure of the fluid supplied to the motor rises above a predetermined value owing to the resistance offered thereto by the decelerating mechanism.

Reference will now be made to the accompanying drawings in which:

FIGURE 1 is a simplified side elevation of a turret lathe incorporating an example of the invention;

FIGURE 2 is an enlarged fragmentary section on line 22 through the headstock of the lathe shown in FIG- URE 1;

FIGURE 3 is a somewhat diagrammatic sectional view taken on line 33 in FIGURE 2;

FIGURE 3a is a section on line Bra-3a in FIGURE 3;

FIGURE 4 is a plan view of what is shown in FIG- URES 2 and 3 with parts of the headstock casing removed and/ or sectioned to expose the interior thereof;

FIGURE 5 is a fragmentary sectional view on line 5-5 in FIGURE 4;

FIGURES 6 and 7 are sectional views on line 6-6 in FIGURE 2 taken looking in opposite directions;

FIGURE 8 is a fragmentary sectional view on line 8-S in FIGURE 4;

FIGURE 9 is a fragmentary sectional view on line 9-9 in FIGURE 4;

FIGURE 10 is a fragmentary sectional view on line Iii-4th in FIGURE 2; and

FIGURE 11 is a diagrammatic view showing the electrical and hydraulic circuit arrangements of the transmission described.

In an example of the invention a change-speed power transmission mechanism is employed to drive the spindle 26 of a turret lathe 21. The mechanism is arranged to provide twelve spindle speeds in each direction, as well as a free spindle condition. The drive is transmitted from an input member, in the form of pulley 24 which is connected by a belt drive 22 to motor 23, to an input shaft, through the intermediary of an hydraulically operable clutch 25. The clutch is of the friction plate type in which the various plates are clamped together, when it is required to trans- 56 is splined at i from the ends of the cylinder and an mit a drive, by an hydraulically operable thrust piston 26 mounted in an annular clutch cylinder 27. A brake 28 is also provided on the input shaft, the brake being of similar construction to the clutch and having one set of plates connected to a fixed part 29 of the headstock.

Slidably mounted on a splined part of the input shaft 30 is a toothed control member 31 comprising gear wheels 32, 33 and 34 of different sizes. The first toothed control member is axially movable between first, second and third positions and in these positions respectively the three gear wheels 32;, 33 and 34 engage gear Wheels 35, 36 and 37 respectively. These latter gear wheels are splined to a lay shaft 38 which is spaced from and parallel to the input shaft 3%). This lay shaft 38 can therefore be driven at three different speeds relative to the input shaft.

Splined to a lay shaft 39 which is equally spaced from and parallel to both the input shaft 30 and the lay shaft 38, is a toothed control member 40 which has at one end a gear wheel 41 engagea'ble with the gear wheel 35 when the member Ell occupies a first position. The other end of member 4 3 is externally splined at 4-2 so that when moved to a second position it can enter a splined hole 43 in gear wheel .4 rotata-bly mounted on lay shaft 39. This gear wheel 54 is continuously in mesh with a gear wheel 45' splined to lay shaft 38. Lay shaft 39 is thus drivable at two alternative speeds relative to lay shaft 38 and at six different speeds relative to the input shaft Bil.

Another splined part of the lay shaft 39 carries a toothed control member 46 comprising gear wheels 47 and 43. Gear wheel 47 is engagea-ble, when member 46 is moved to a first position with an equal gear wheel 49 which is rotatable on a lay shaft 51) coaxial with the lay shaft 33. Gear wheel 48 is engageable, when member 46 is moved to a second position, with a gear wheel 51 keyed to a lay shaft 52 coaxial with the input shaft 30, gear wheel 51 being also engaged with a gear wheel 53 of the same size as gear Wheel 48 and secured to the gear wheel 49. Shaft 52 is thereby drivable either forwardly or rearwardly at siX speeds.

Lay shaft has an output gear 54 splined to one of its ends, this gear being engaged with a coacting gear 55 on the head stock spindle 20 which thereby forms the output member of the transmission. An axially slidable toothed control member 56 is provided on a splined part of the lay shaft 50 and this has a splined recess 57 at one end adapted to receive the teeth of gear wheel 53 when member 56 is moved to a first position. In forward drive lay shaft 52 then takes no part in the transmission. In reverse, however, gear wheel 51 is interposed to reverse the direction of drive. The other end of control member 58 so that when moved to a second position, it enters a splined hole 60 in a gear wheel 59 rotatable on lay shaft 50 and engaging a gear 61 on lay shaft 52 so as to provide an additional reduction step. The spindle 20 can therefore be driven at twelve different speeds in each direction.

Four hydraulic cylinder units 62, 63, 64, 65 are employed to shift the four toothed control members 56, 31, 40 and 46 respectively. The units 62, 64 associated with members 56 and 40 are each in the form of a simple hydraulic ram with a port at each end. The other two units, however (as shown in FIGURE 5 and which illustrates unit 63) each comprise a stepped cylinder having therein a piston 66 slidable in the smaller portion 67 of the cylinder, a piston rod 68 secured to the piston and projecting annular free piston 69 slidable in the larger part 70 of the cylinder and on the piston rod 68. Each cylinder has a port at each end and a central port adjacent the step in the cylinder. The toothed control members 40, 46 are linked to their respective hydraulic cylinder units 64, 65 by a pair of pivoted levers 71, 72 respectively, Whilst forlcs 73, 74 secured directly to the ends of the piston rods of the other units 62, 63 engage the other two toothed control members 31, 56. The cylinder units are formed in a common cylinder block 75.

The supply of liquid to the cylinder units 62 to 65 controlling the toothed control members is controlled by a selector valve 78 mounted on the cylinder block 7 5. This selector valve 76 includes a body 77 formed with a shallow cylindrical chamber 77a. Mounted in this chamber is a circular valve plate 78 which is provided around its periphery with a sealing ring 780 engaged with the chamber wall. The valve plate 78 is formed with a central splined hole and is free to slide axially on a splined operating spindle 80 projecting into the chamber through the body wall. The selector valve also includes a circular port plate 81 in which are formed seven ports 81a to 81g. These ports are disposed at different distances from the centre of the port plates 81 and are connected respectively to ports of the cylinder units 62, 63 and 64 controlling toothed controlled members 56, 31 and 40 via grooves 75a in the surface of cylinder block 75 on which plate 81 is clamped. The valve plate 78 is also formed with a plurality of bores 78a which are a'lignable with the ports 81a to 81g. These bores 7 8a are so arranged that in twelve equiangularly spaced positions of the valve plate 78, twelve different combinations of connections between the ports and the interior of the chambers 77:: are achieved.

A supply line '79, to be referred to further hereinafter, opens into the chamber 77a so that When pressurised liquid is present in this line the pressure will be communicated to those ports 81a to 81g which are aligned with bores 78a in the valve plate 78. The side of the valve plate '78 adjacent of the port plate 81 is formed with recesses 78b surrounding the various bores. These recesses are interconnected and are connected to the edge of the valve plate '78. The body, moreover, is formed with one or more drain ports 76a which are disposed at the end of the body remote from the chamber 77a. These drain ports 76a enable the liquid in the space between the valve plate 78 and port plate 81 to remain at low pressure and it Will be appreciated that any ports 81a to 81g not aligned with bores 78a in the valve plate 78 will open into this space.

Thus, in use, whilst the mechanism is running a gear change can be preselected by adjusting the selector valve 76 to supply liquid to the cylinder units 62 to 64 and thereby to move the toothed control members to new positions. Such movement of the selector valve 76 can only be effected, however, when pressure in the supply line 79 is low and insufilcient to affect the cylinder units 62 to 64, since, when the pressure in the supply line is high the valve plate 78 Will be thrust into engagement with the port plate 81 owing to the difference in pressure between the liquid in the chamber 77a and the liquid in the space between the valve plate 78 and the port plate 81. Thus, when it is possible to adjust the selector valve 76 no gear change will take place until there is a rise in pressure in the supply line 79.

Where, as is the case in the example described, the selector valve 76 is disposed in a somewhat inaccessible position, this may be actuated by a remote control device 82 through the intermediary of a connecting rod 83 and bevel gearing 84. The connections 85, 86 between the rod and the control device and between the rod and the bevel gearing are conveniently of the universal kind.

The supply of liquid to the cylinder unit 65 of member 46, which determines whether the lathe spindle is rotated forwardly, rearwardly or left free, is controlled by first and second solenoid valves 87, 88. The first of these valves has an inlet port 87a connected to the aforementioned supply line '79 and an outlet port 8712 connected to drain as well as a supply port 870 connected to the port 65a at that end of the cylinder unit 65 from which liquid will flow when the member 46 is moved to its first position. This valve is arranged so that the supply port 87c is normally connected to the supply line 79. The second valve 88 is a simple reversing valve with inlet and outlet ports 88a, 88b connected to the supply line 79 and drain respectively and with a pair of supply ports 88c, 88d connected respectively to the step port 65b and the other end port 65c of the cylinder unit 65. This second valve 88 is arranged so that said other end port 650 is normally connected to the supply line '79. Thus when there is pressure in the supply line 79 and neither of the solenoid valves 87, 88 is operated control member 46 will occupy a free spindle position since the same pressure will be applied to the piston 6501 in one direction and to the larger free piston 65a in the opposite direction. From this position operation of the first solenoid valve 87 will cause control member 46 to be moved to its first position (to provide forward drive) provided that pressure is present in the supply line 79, and operation of both valves will cause it to be moved to its second position (to provide reverse drive).

The control of the pressure in the supply line 79 is effected by first and second hydraulically operable valves 89, 90. The first of these is a simple reversing valve 89 having four ports one of which (89a) is connected to the supply line 79 and two more of which (8915, 89c) are connected respectively to an input line 91 (to be further described hereinafter) and to the supply port a of the second hydraulically operable valve 90. The first hydraulically operable valve 88 is provided with a snap action device 92 and its spool is movable in one direction by pressure in a sensing line 93. This spool is movable in the opposite direction by a return 'device 94 including the above mentioned snap action device 42 which may conveniently include a plunger 95 with a pair of axially spaced grooves into which spring loaded balls 96 are pressed to hold the spool in position when no pressure is applied in either direction. After the return device 92 has been actuated the connections to the valve are such that the supply line 79 is connected to the second hydraulically operable valve 90. The second hydraulically operable valve 90 is spring loaded and has a further pair of ports 98b, 900 connected to the input line and drain respectively. The arrangement of this is such that in the normal position of the valve the input line 91 is stopped and the supply port 90a is connected to drain and in the other position the drain port 90c is stopped whilst the supply port 90a is connected to the input line 91. The second hydraulically operable valve is sensitive to the pressure in the sensing line 93 to which it is connected through an additional pair of ports 87d, 87a of the first solenoid valve. These additional ports are arranged so that when the solenoid is de-energised the second hydraulically operable valve 90 is connected to the sensing line 93 whereas on energisation this connection is stopped and the valve 98 is connected to drain.

The pressure in the sensing line 93 is determined by the speed of the input shaft 36 of the gear box, since this is connected, through a reduction gear train and a unidirectional clutch 97 to a vane-type fixed displacement hydraulic motor 98 (see FIGURE 10). The unidirectional clutch 97 is arranged so that the input shaft 30 cannot drive the motor 98 and the latter is supplied with liquid, in use, at an insufiicient rate for the motor 98 to drive the input shaft. A separate pump 100 is provided for this purpose and may, if desired, also be employed to supply oil to the lubricating system of the lathe. To the conduit supplying oil to the motor 98 the aforesaid sensing line is connected.

Thus it will be realised that, when the clutch 25 is disengaged and the brake 28 engaged, to start a gear change after the next speed has been selected, the input shaft 30 will be slowed down until the hydraulic motor 98 starts to drive the input shaft. The pressure in the sensing line 93 will then start to rise until it is sufficient to operate the first hydraulically operable valve 80. The

second hydraulically operable valve 90 will also be operated provided that the first solenoid valve 87 has not been energised. It will be noted that operation of the first hydraulically operable valve 39 causes the input line 91 to be connected to the supply line 79 so that a preselected gear change will commence. It will also be noted that, if both the clutch 25 and the brake 28 are disengaged as the toothed control members are moved into engagement with the various co-acting parts, the hydraulic motor 98 will drive the gears slowly so that tooth to tooth engagement-obviously highly undesirable-is prevented.

The remaining port 8% of the four-ported first hydraulically operable valve (of which only three ports have so far been mentioned) is connected in the part of the hydraulic circuit for operating the brake 28. This port 89d is connected to an inlet port 101a of a six-ported two position third solenoid valve 101 of which another port 10112 is connected to drain, another 1010 to the main pump 102 and another 101d to a manual control valve 103 (to be described hereinafter). The two outlet ports 101e and 101] of this third hydraulically operable valve 101 are connected respectively to the brake cylinder 28 and to the actuator of a third hydraulically operable valve 104. Thus, during a gear change so long as this third solenoid valve 101 is not energised the condition of the brake 25 will be determined by the first hydraulically operable valve 89 and this will connect it to drain or the input line 91 depending the pressure in the sensing line 93. Operation of the third solenoid valve 101 stops the first mentioned port 101:! and that connected to drain and connects the other two inlet ports 1011), 101d to the two outlet ports 101 and 1012.

The third hydraulically operable valve 104 controls the supply of liquid to the clutch 25 and to the input line 91. The valve has six portsone, 104a, to the clutch cylinder 25, a second 104]), to drain, a third, 104a, to the main pump 102, a fourth, 104d, to the supply line 91 and fifth and sixth 1042, -1 to different parts of the manual control valve 103. The fifth port 1042 is also connected to the return device 94 of the first hydraulically operable valve 89. The valve 104 is spring loaded to a normal position in which the first and second ports 104a, 1041) are interconnected, the third and fourth ports 1040, 104d are interconnected and the other two ports 104e, 101 are stopped. On actuation the valve 104- changes over to a condition in which the first and fifth ports 104a, 1042 are interconnected, the second and fourth ports 104b, 104d are interconnected and the third-21nd sixth ports 1040, 104 are interconnected.

The valves 87, S9, 09, 90, 101 and 104 are all mounted in a common block 105 mounted on a part 106 of the headstock casing. Connections between the valves are made by grooves in both faces of a plate 107. The connection to clutch 25, brake 26 and motor 98 are made by bores 108, 109 and 110 in a part 111 of the casing, which bores communicate with tubes 112, 113 and 114 extending through the hollow input shaft 30.

The three solenoid valves 87, 88 and 101 are operable respectively by contacts 115b, 1160, 11712 of first, second and third relays 115, 116, 117. These relays are in turn controlled respectively by a first switch 118, a second switch 119 and a pressure switch 120 in an accumulator 121 subjected to supply line pressure. Each of the relays 115, 116, 117 has latching contacts 115a, 116a, 117a and the second relay also has an additional set of contacts 11% for operating the first relay 115. A third switch 122 is also provided for selecting a free-spindle condition.

The aforementioned manual control valve 103 is brought into the circuit only at the completion of a gear change-Le. when the third hydraulic valve 104 and the third solenoid valve 101 are both operated and the supply line 79 is exhausted through the first and second hydraulic valves 89, 90. This valve 103 (see FIGURE 8) includes a body "23 in which a longitudinal bore is formed. Mount ed within this bore are four orifice plates 124 each of which is in the form of a thick disc formed with a central cylindrical recess. The base of the recess in each orifice plate is formed with the orifice 124a itself. Each plate also has an external groove housing a sealing ring 125. Moreover the ends of the body bore are closed 011 so that the four orifices divide the body into five chambers. Formed in the body and orifice plates are five ports which communicate with the chambers respectively. The two outermost ports 126, 127 are drain ports and these are connected to drain. The central port 128 (see FIGURE 4) is the inlet port and receives high pressure liquid whenever the third hydraulically operable valve 104 is operated. The remaining two ports 129, 130 are connected respectively to the third solenoid valve 104 and the third hydraulically operable valve 104- .and supply liquid to the brake 23 and the clutch 25 respectively when these valves are operated.

The manual control valve has an operating member in the form of a shaped needle 131 which extends through the four orifices 124. This needle has three waisted portions from each of which it expands frusto-conically in each axial direction. The needle 131 is so shaped that in it will completely close the first and the other extreme position it completely closes the second and fourth orifices. Moreover, when the needle 131 is mid-way between its extreme positions all four orifices will be open to the same extent. Thus slight axial movement of the needle out of the midposition will cause a change in flow through the valve. The needle 131 is axially movable by a lateral projection 132 or an operating piece secured to one of its ends, said projection extending into a helical slot 133 in the body and being connected to an operating handle 134. Alternatively axial movement may be achieved by a push-rod or otherwise.

The mechanism is so arranged that when the needle 131 of the manual control valve 103 is in its mid-position neither the clutch 25 nor the brake 28 is fully engaged and the operator, by careful manipulation of the control can run the spindle 20 at a very low speed so that he can inspect work in the lathe or for other purposes.

When the lathe is first started up the three relays 115, 116, 117 are initially all tie-energized. The two pumps 102, 102 and the drive 23 to the input pulley 25 are all started. The brake 28 is applied by liquid supplied from the main pump 102 through the third hydraulic valve motor 98 cannot be driven and pressure in the sensing line 93 rises until the first and second hydraulic valves 09, are operated. Liquid is then supplied to the brake 28 through the third hydraulic valve 104, the input line 91, the second hydraulic valve 90, the first hydraulic valve 89 and the third solenoid valve 101 in series. At the same time liquid from the input line 91 passes through the first hydraulic valve 89 to the supply line 79 and thence through the first solenoid valve 87 and the second solenoid valve 88 to both end ports, 650, 650 of the cylinder unit 65 of toothed control member 46. The supply line 79 also carries liquid to the pre-set selector valve 76 and any necessary gear shifts are effected.

When the gear change is completed the pressure in the supply line 79 rises since flow has ceased. The pressure switch is thus actuated and the third relay 117 energises the third solenoid valve 101. Liquid passes through the valve 101 and operates the third hydraulic valve 104. The course of events following this action depends upon the state of the manual control valve 103. If this has been orifices then lay shafts 38, 39

the hydraulic motor 98 will remain stationary and the pressure in the sensing line 93 will remain high so that no further changes occur. If the valve 103 is set to operate the clutch 25, however, or when such a setting is selected, the input shaft 30 will rotate, allowing the pressure in the sensing line 93 to drop. The first and second hydraulic valves 89, 9% are then returned to their initial positions.

If the first switch 113 is now operated to select forward running and a new spindle speed has been selected on the selector valve 76, the third relay 117 is de-energised and the first relay 115 is energised. Thus the third solenoid valve 101 returns to its original position so cutting off the supply to the actuator of the third hydraulic valve 104 which also returns to its initial condition. The clutch 25 is thereby disengaged and the brake 28 engaged so that the machine slows down. The pressure in the sensing line 76 rises as soon as the hydraulic motor 98 is forced to take over driving, but since the first solenoid valve 87 has been operated by the first relay 115, only the first hydraulic valve 89 is changed over, the second hydraulic valve 90 remaining in its initial position. Liquid then flows to said other end port 650 of the cylinder unit 65 of toothed control member 46 and this is moved to its first position. Meanwhile flow through the selector valve 7 6 causes the other toothed control members to be moved as required. During the actual gear change the brake 28 is released as its cylinder is connected to drain through the third solenoid valve 101, the first hydraulic valve 39 and the second hydraulic valve 90 in series and the hydraulic motor 98 therefore turns the shafts at a low speed to prevent tooth to tooth engagement. The completion of the change is again signalled by a rise in pressure in the supply line 79 so that the pressure switch 120 is operated .and the third relay 117 operates the third solenoid valve 101 as before.

Similar sequence of events occur when the second and third switches are actuated with the respective results of reverse running and free spindle.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is:

1. A change-speed power transmission mechanism comprising an input member, a driving shaft, means for drivingly interconnecting the input member and the driving shaft and including a clutch, a driven shaft, means drivingly connecting said driven shaft to an output member, a toothed control member on one of said shafts and axially movable between first and second positions to provide first and second speed ratios respectively, a fluid operable motor connected to the output side of said clutch, through the intermediary of a unidirectional drive device arranged so that, in use, no drive is transmitted from said clutch to said motor, a pump for supplying operating fluid to said motor to drive the latter, means sensitive to the pressure at which fluid is supplied to the motor and means operable by said pressure-sensitive means for moving said toothed control member when the clutch is disengaged and the pressure of the fluid supplied to the motor rises above a predetermined value owing to the resistance offered thereto by the decelerating mechanism.

' 2. A mechanism as claimed in claim 1 in which said means for moving said toothed control member is fluid pressure operated and said means sensitive to the pressure at which fluid is supplied to said motor comprises a valve adapted to be operated by a fluid pressure in excess of said predetermined value.

3. A mechanism as claimed in claim 2 in which means are provided for re-engaging the clutch after completion of the movement of said toothed control member.

4. A mechanism as claimed in claim 3 in which said means for re-engaging the clutch comprises a device sensitive to the pressure of fluid supplied to said fluid pressure operated means for moving the toothed control member and adapted to be operated by the rise in such pressure which occurs when the toothed control member reaches the end of its movement.

5. A mechanism as claimed in claim 4 and in which said device controls a valve which itself controls flow of fluid to fluid operated means for engaging the clutch.

6. A mechanism as claimed in claim 5 in which said valve is controlled by said device through the intermediary of a further valve which also controls the supply of fluid to a fluid operated brake capable of acting to stop the input shaft.

7. A mechanism as claimed in claim 1 wherein said toothed control member is movable between three alternative positions and said means for moving the toothed control member comprises a stepped cylinder, a piston slidable in the cylinder, .a piston rod projecting from the cylinder and connected to the toothed control member, an annular piston slidable in a large-r portion of the cylinder and surrounding the piston rods, and inlet ports to the cylinder at opposite ends and at a position intermediate the ends so that supplying of pressurised fluid to the port intermediate the ends causes the pistons to be separated.

8. A mechanism as claimed in claim 7 wherein the toothed control member is movable to cause the output shaft to be driven forwardly, rearwardly or remain free from connection to the input shaft according to the position of the toothed control member.

9. A mechanism as claimed in claim 7 in which the supply of fluid to the ports of the stepped cylinder is controlled by a pair of independently operable valves, arranged so that when neither valve has been actuated pressurised fluid can be supplied to both end ports of the cylinder to retain the toothed control member in an intermediate position, when one valve has been actuated fluid can be supplied to one end port and the intermediate port to move the toothed control member to a first position, and when both valves have been actuated fluid can be supplied to the other end port and the intermediate port to move the toothed control member to a second position.

10. A mechanism as claimed in claim 7 in which the supply of fluid to ports of the cylinder is under the control of a single selector valve.

1d. A mechanism as claim in claim 1 incorporating a plurality of toothed control members each movable between a plurality of different positions to enable a multiplicity of different speed ratios to be established between the input shaft and the output shaft and a plurality of selectively operable fluid operated units for moving said toothed control members.

12. A mechanism as claimed in claim 11 in which one of said toothed control members is movable to determine whether the output shaft is driven forwardly or rearwardly or remains free from driving connection with said input shaft, the remaining toothed cont-r01 members being movable to determinenthe speed ratio between the input shaft and the output shaft.

13. A mechanism as claimed in claim 12 incorporating a selector valve which determines to which of the units associated with said remaining toothed control members fluid pressure can be applied.

14. A mechanism as claimed in claim 13 in which the selector valve includes a port plate having ports equal in number to the total number of ports possessed by said units associated with said remaining toothed control members and connected respectively to said ports, and a valve plate movable over the surface of the port plate and formed with bores alignable with selected ones of the ports in the port plate whereby pressurised fluid can flow through the aligned bores and ports to operate said units.

15. A mechanism as claimed in claim 14 in which said valve plate is contained within a chamber and is arranged so that when fluid pressure is applied to said units the same pressure urges the valve plate against the port plate to prevent adjustment of the position of the valve plate.

16. A mechanism as claimed in claim 1, and another pump which supplies fluid to the clutch and the fluid pressure operated means for moving the toothed control member.

17. A mechanism as claimed in claim 16 including a fluid pressure operated brake for stopping the input shaft, and said other pump connected to said brake for supplying fluid to same.

18. A mechanism as claimed in claim 11 including a brake, valves operable at the completion of the movement of the toothed control member and connected to control the supply of fluid to said brake and to said clutch, said valve also controlling a connection to clutch and brake circuits which include a manual control valve operable to vary the engagement of said brake and clutch.

19. A mechanism as claimed in claim 18 in which said manually operable valve incorporates an operating member movable between a first position in which the clutch is fully engaged and the brake is disengaged and a second position in which the brake is fully engaged References Cited UNITED STATES PATENTS 2,501,286 3/1950 Mirossay 192-3.5 X 2,537,409 1/1951 Hassman et a1. 192--3.5 2,555,242 5/1951 Nenninger et a1. l923.5 X 3,089,572 5/1963 Herfurth 192-3.5

BENJAMIN W. WYCHE III, Primary Examiner. 

1. A CHANGE-SPEED POWER TRANSMISSION MECHANISM COMPRISING AN INPUT MEMBER, A DRIVING SHAFT, MEANS FOR DRIVINGLY INTERCONNECTING THE INPUT MEMBER AND THE DRIVING SHAFT AND INCLUDING A CLUTCH, A DRIVEN SHAFT, MEANS DRIVINGLY CONNECTING SAID DRIVEN SHAFT TO AN OUTPUT MEMBER, A TOOTHED CONTROL MEMBER ON ONE OF SAID SHAFTS AND AXIALLY MOVABLE BETWEEN FIRST AND SECOND POSITIONS TO PROVIDE FIRST AND SECOND SPEED RATIOS RESPECTIVELY, A FLUID OPERABLE MOTOR CONNECTED TO THE OUTPUT SIDE OF SAID CLUTCH, THROUGH THE INTERMEDIARY OF A UNIDIRECTIONAL DRIVE DEVICE ARRANGED SO THAT, IN USE, NO DRIVE IS TRANSMITTED FROM SAID CLUTCH TO SAID MOTOR, A PUMP FOR SUPPLYING OPERATING FLUID TO SAID MOTOR TO DRIVE THE LATTER, MEANS SENSITIVE TO THE PRESSURE AT WHICH FLUID IS SUPPLIED TO THE MOTOR AND MEANS OPERABLE BY SAID PRESSURE-SENSITIVE MEANS FOR MOVING SAID TOOTHED CONTROL MEMBER WHEN THE CLUTCH IS DISENGAGED AND THE PRESSURE OF THE FLUID SUPPLIED TO THE MOTOR RISES ABOVE A PREDETERMINED VALUE OWING TO THE RESISTANCE OFFERED THEREBY BY THE DECELERATING MECHANISM. 